1. Field of the Invention
The present invention relates to metal separators, and more particularly to an apparatus for separating non-ferrous metal pieces from ferrous metals, rocks, glass, rubber, wood and dirt.
2. Description of the Related Art
In this present era of recycling and limited land-fill space, the necessity to reclaim reusable materials from debris and waste has become of the utmost concern to our society. The reclamation of metal materials is additionally important due to the increasing scarcity of these natural resources and the cost-effectiveness of recycling versus mining and purification of metals. To recover metals from debris and waste, the recycling industry has developed numerous metal separating devices.
Ferrous metal pieces are easily removed by suitable magnets which remove the ferrous metals from the debris using attractive magnetic forces to pull the ferrous metals from the debris material. Non-ferrous metals must be removed using alternative methods since they do not contain the magnetic properties of ferrous metals. To remove non-ferrous metals from debris, the recycling industry has developed metal separators that subject the non-ferrous metal materials to a high density, rapidly changing, magnetic flux fields, which induces eddy currents in electrically conductive non-ferrous metal materials. The eddy currents create a repulsive magnetic force in the materials which allows the materials to travel away from the magnetic flux field and consequentially be separated from non-electrically conductive materials in the debris. The magnitude of this repulsive magnetic force is defined by the electrical resistivity of the metal, size and shape of the material, magnetic flux field strength and the velocity and frequency of the rotating magnetic poles creating the magnetic flux field.
Prior devices utilizing the eddy current concept to separate non-ferrous metals from debris have transported the debris along a conveyor belt on which a rotating drum containing the magnetic poles is positioned to rotate in the same plane as the conveyor belt and at the end of the conveyor belt. In this way, the non-ferrous metals are repulsed further away from the other materials in the debris as all the materials in the debris are projected from the conveyor belt. The prior art discloses several inventions embodying this device. Benson, U.S. Pat. No. 5,080,234, utilizes a pair of cylinders, one above the other, rotated synchronously in opposite directions and matched so that the poles of opposite polarity face each other across an air gap. As electrically conductive particles are conveyed across the gap, an eddy current is induced in the particles and they are separated and collected apart from the free falling non-conductive materials in the debris.
Applying the same eddy current principles as Benson is Feistner et al, U.S. Pat. No. 5,092,986. Feistner et al places a rotating drum consisting of magnets, eccentric to a belt drum on which debris is conveyed. Eddy currents are created in electrically conducive particles of the debris as they are conveyed over the rotating drum and through the magnetic flux field. These particles are projected further off a conveyor belt by the repulsive magnetic force. This allows the electrically conductive particles to be separated from the other debris materials. Feistner et al also employs a scraper to remove iron particles, which are attracted to the magnets, from the belt drum to prevent damage. Wolanski et al, U.S. Pat. No. 4,869,811, and Kauppila et al, U.S. Pat. No. 5,236,091, disclose similar eddy current separators as described in the aforementioned patents.
By using horizontally mounted magnetic drums to create a magnetic flux field, the horizontally mounted magnetic drum must rotate at between 1800 to 3500 rotations per minute (RPM) in order to create a strong enough magnetic flux field to induce an eddy current in the non-ferrous metal particles. In order to maintain these high RPMs, a strong motor which consumes extensive energy must be utilized by the separator machine.
In the prior art, the use of horizontally mounted magnetic drums increases the distance between the magnets and the debris which results in the need for greater RPMs to compensate for a decrease in the magnetic field flux strength due to the increased distance. Current separator machines only provide one opportunity for the non-ferrous metal materials to be acted on by the magnetic field flux. This single opportunity results in the possibility of some non-ferrous metal materials not being removed from the other debris materials or the need to rerun the debris through the separator machine. These disadvantages need to be alleviated, in order to make separator machines as cost-effective and as efficient as possible.